Question: The equation of an ellipse $E$ is $\dfrac {(x+9)^{2}}{25}+\dfrac {(y+1)^{2}}{9} = 1$. What are its center $(h, k)$ and its major and minor radius?
The equation of an ellipse with center $(h, k)$ is $ \dfrac{(x - h)^2}{a^2} + \dfrac{(y - k)^2}{b^2} = 1$ We can rewrite the given equation as $\dfrac{(x - (-9))^2}{25} + \dfrac{(y - (-1))^2}{9} = 1 $ Thus, the center $(h, k) = (-9, -1)$ $25$ is bigger than $9$ so the major radius is $\sqrt{25} = 5$ and the minor radius is $\sqrt{9} = 3$.